Mechanical compressors and expanders (e.g., engines, pumps, or the like) compress or expand a compressible fluid for a variety of functions. With compressors, the fluid is compressed to compactly store the fluid under high pressure for later use, such as compressed air for pneumatic tools. Typical mechanical compressors and expanders use cylinder and piston arrangements to compress or expand the fluid. Liquid pistons are used in some examples as compressors or expanders. The liquid piston fluid is formed along the face of a driven piston and provides an interface with the compressible fluid. As a compressor, the liquid piston moves relative to the cylinder to compress the compressible fluid. Conversely, as an expander (engine, motor, etc.) the compressible fluid moves the liquid piston relative to the cylinder to generate mechanical power that can be used, for example, to rotate a shaft.
One issue with the use of such liquid pistons that are positioned between the driven piston face and the compressible fluid, is that the interface between the liquid piston fluid and the compressible fluid can be subject to disturbances that can adversely affect the performance of the compressor or expander. For instance, when a liquid piston operates at relatively high frequencies that exceed one gravity of liquid piston deceleration, the liquid piston fluid is readily disturbed by the movement of the piston including acceleration and deceleration. This can cause the liquid piston fluid to be splashed along the cylinder walls and into the cylinder chamber, subjecting the liquid piston fluid to be withdrawn from the cylinder in place of the compressed or expanded compressible fluid, and adversely affecting the system efficiency. Additionally, this extraction of the liquid piston fluid decreases the volume of the liquid piston, resulting in an increase in the cylinder cavity volume. This change in the cylinder cavity volume adversely affects the compression ratio of a compressor, and the energy output produced by an expander.